Hi Michael,
The most common routes for mounting are either atop the rifles scope or attached to the stock underneath or to the side.
Fixing to the barrel is not necessarily the best method as a free floating barrel will droop if you put weight on it and over range, this drop in the point of impact could result in a miss or worse a wound.
It will also impart most shock than the other routes.
The Deft head is light enough on its own to act as a top mounted gun light if one could separate the head from the battery tube and as the DEFT runs long time on eneloop AA's, it would not be difficult to rig up an in line battery pack and slip in a tape switch to boot.
However, the DEFT does have one drawback BECAUSE it is so damned efficient and that is a rifle is capable of very close to very long range depending on the calibre and how much fuel it has poked up its backside !!!!!!.
The beam of the deft would probably need adjusting between very close shots and long stuff coz that lil ol beam is tighter than a ground squirrels bum cheeks when up close.
Its simply too tight.
The likes of the A10G R2 (by way of example) has decent throw but also decent(ish) spill.
The importance of the light is not only to illuminate the quarry BUT to see what is behind it as this is likely where your round will be heading after it has struck. You got to know your round will be absorbed by the backstop behind the quarry in case you miss or you get shoot through.
The final consideration is elevation. the bigger the head the higher it has to be raised above the scope. Things can get a bit top heavy and the deft is unlikely to be used for endoscopy work if we are honest !!!!!!
It has a very wide grin
Similar to the one I had on my face the very first time I switched it on in the dark and similar to the one I have on my face when someone see the deft lit up for the first time.